It is recognized at this stage of the petroleum refining industry that heavy oils such as residual portions of crude oils and reduced crudes boiling above 343.degree. C. (650.degree. F.) comprising Conradson carbon producing components including asphaltenes and porphyrins boiling above about 552.degree. C. (1025.degree. F.) are less than desirable charge stocks in a normal gas oil catalytic cracking operation because the Conradson carbon producing components and metal contaminants rapidly reduce the catalyst cracking activity and selectivity as well as cause undesired yields of dry gas and coke at the expense of desired gasoline boiling range products.
Crude oils comprising metallo-organic compounds are known in which from 30 to 60 percent or more by volume comprise compounds boiling above about 343.degree. C. (650.degree. F.) with from about 10 to 30 volume percent of the total crude volume comprising compounds boiling above about 552.degree. C. or 566.degree. C. (1025.degree. F. or 1050.degree. F.) at atmospheric pressure. Because of the scarcity of high quality gas oils boiling in the range of 343.degree. C. (650.degree. F.) up to about 552.degree. C. (1025.degree. F.), it is now necessary to develop economical and efficient processes for converting residual oils, reduced crudes and more of the crude barrel to desired products of gasoline, gasoline precursors and light fuel oils.
It is also important economically to be able to employ existing processing equipment such as gas oil fluid catalytic cracking processing equipment for converting the less desirable residual oil feed stocks in the absence of major modification and reconstruction of existing equipment. That is, it is particularly desirable to offset the destructive effects of metal contaminants and high Conradson carbon feeds by employing some modified processing parameters rather than effecting major equipment changes. More important is the need to achieve conversion of more of the crude barrel to gasoline and gasoline precursors than obtainable with a more clean gas oil feed as accomplished in existing fluid catalytic cracking (FCC) operations.
Crude oils in the natural state contain a variety of metallo-organic compounds which contribute to undesirable catalyst functions in cracking the heaviest or resid portion of a crude oil. Among these compounds are coke precursors (asphaltenes, poly-nuclear aromatics of at least 5 rings); heavy metals such as iron, nickel, vanadium and copper as free metals, oxides and sulfides or combined as porphyrins in combination with deactivating amounts of sodium, potassium, sulfur and nitrogen materials. Materials such as high boiling asphaltenes tend to break down into coke during the cracking operation which deposits on the catalyst as carbonaceous or hydrocarbonaceous material thereby inactivating the catalyst cracking activity and particularly its selectivity. Metal deposits further contribute to this inactivation of catalyst particles beyond simple restoration techniques and such metals deposition can cause terminal deactivation of a crystalline zeolite structure employed in a cracking catalyst. It has been determined that the heavy metals transfer almost quantitatively from the feed stock to a catalyst particle surface.
Numerous proposals are provided in the prior art for upgrading poor quality residual oil feeds to obtain desired gasoline products. These proposals include the combination of one or more of vacuum distillation solvent extraction, hydrotreating, thermal visbreaking in combination with catalytic cracking and combinations thereof, all of which are criticized as economically unattractive for processing high cost crude oil and particularly that of poor quality.
A number of patents in the prior art disclose the concept of passivating metal contaminants of nickel, vanadium, copper and iron by the addition of metals and compounds thereof selected from the group of magnesium, calcium, strontium, barium, scandium, titanium, chromium, molybdenium, manganese, cobalt, antimony, zinc, cadmium, zirconium, tin, lead and rare earth metals, all of which may or may not contribute to altering product selectivity in a fluid catalytic cracking operation.
It is clear from the above that innovative if not dramatic processing contributions are desperately needed at this stage of the petroleum refining industry. The present invention is directed to a new and novel combination of fluid catalytic cracking processing restrictions and operating parameters which amount to a giant step forward in the catalytic conversion of reduced crudes to gasoline, gasoline precursors and higher boiling liquids and reducing problems associated with the production of gasoline, fuel oils and gasoline precursors from poor quality crudes.
The present invention further addresses itself to obtaining an efficient and economically attractive heat balanced operation for upgrading poor quality crude oils comprising residual portions of crude oils including atmospheric gas oils and higher boiling portions thereof known as vacuum gas oils and vacuum resid boiling above about 552.degree. C. (1025.degree. F.) to produce gasoline and other useful products. The present invention is also directed to a combination of operating parmameters by which the catalyst operating life is retained for an extended on-stream life during conversion of poor quality residual oils comprising components boiling above 552.degree. C. (1025.degree. F.).